There's no way around it: To generate the energy we need to live, our cells have to burn fuel. And like a fire, the reactions that take place in each cell produce potentially damaging by-products. The process is known as oxidation.

Normally, the body reacts quickly to repair any damage the by-products cause. "It's generally counteracted by antioxidants like vitamin E and vitamin C. But when the system is overrun, it may not be able to handle the load," says University of Tennessee Health Science Center researcher Abbas Kitabchi, PhD, MD, FACP, FACE.

Obesity in particular can make the job harder, leading to higher levels of what's called oxidative stress. In turn, oxidative stress causes some of the conditions associated with overweight, like cardiovascular disease and inflammation. The fat that causes oxidative stress is some of the hardest to lose. "It's been clearly shown that you decrease oxidative stress if you lose more fat [and] you are overweight. What we are talking about is inside the abdominal cavity—it's the type of fat liposuction won'' help," Kitabchi says. "Anything we could do to attenuate these problems would be of great value to people."

It stands to reason that losing weight reduces the risks by helping relieve the stresses on the body. But Kitabchi says all weight loss isn't created equal. Studies have shown that diets high in carbohydrates cause more oxidative stress than diets with more protein. Kitabchi wanted to see if the difference could be measured in people who were losing weight.

To find out, Kitabchi is putting two diets head-to-head with the help of a grant from the American Diabetes Association. In one corner is the so-called ADA diet, made up of 55 percent carbohydrates, 15 percent protein, and 30 percent fat. "A group of experts sat down and, by consensus, developed a reasonable diet for people with diabetes," Kitabchi says. "It's fairly well balanced but relatively high-carb."

Its opponent is the Zone Diet, a commercial weight-loss plan with twice as much protein as the ADA diet and just 40 percent carbs. To measure the effects of the two plans, Kitabchi recruited two dozen obese women in the Memphis area between the ages of 20 and 45 for a six-month trial. The decision not to recruit men had a lot to do with streamlining the study. "Usually, we find ladies are more adherent and amenable to coming in on a weekly basis," Kitabchi says. "They're the best group for the study."

Six months' worth of free meals was part of the draw. "To encourage adherence, we provided breakfast, lunch, dinner, and snacks for all these patients," Kitabchi says. At 20 meals a week, that's 480 meals per person. (Participants also got diet snacks and one "free meal" on their own each week.)

The higher-carb ADA diets were mostly commercially available frozen diet meals; for the high-protein Zone Diet, Kitabchi filled three huge freezers with meals purchased from the California company. "They're typical meals—pizza for some of them, cake, steak, spaghetti. We try to provide the type of thing people would eat in general, with certain carbohydrate or protein restrictions."

Before the study began, participants were weighed and had their daily calorie requirements measured. Kitabchi's team then gave each woman 500 calories fewer than she needed per day to maintain her weight. By supplying all their meals, the researchers could calculate exactly how much food participants were consuming. Says Kitabchi: "They come in every week with an insulated bag, and we ask them about their eating habits." Study participants report sticking with the prescribed diet 90 percent of the time.

The calorie restrictions meant that both diets were likely to help with weight loss, of course. But Kitabchi was measuring more than pounds shed. Each week, when study participants came in to collect their bags full of frozen dinners, the researchers measured a host of other indicators, including blood pressure and blood glucose. The goal was to determine whether one diet had more of an impact on indicators of oxidative stress than the other.

Kitabchi is still analyzing the data, but preliminary results are promising. Participants on both diets shed weight, some losing 20 pounds or more over the six-month study. And after as little as one month, Kitabchi and his team measured differences in indicators of oxidative stress between the high-protein and high-carbohydrate diets.

For people with diabetes, Kitabchi's results could help reevaluate the relationship between protein and carbohydrates. In 2009, ADA recognized that low-carb diets could be an effective weight-loss strategy. If studies like Kitabchi's confirm that a low-carb approach offers significant benefits when it comes to reducing oxidative stress and inflammation, it would be vital information for people who are trying to lose weight in the healthiest way possible.

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